Solid propellant gas generators are used in rockets, missiles, interceptors, and various other vehicles and environments. For example, solid propellant gas generators may be used to generate propellant gas for both vehicle propulsion and direction control for missiles, munitions, and various spacecraft. Solid propellant gas generators may also be used to generate propellant gas to drive, for example, a gas turbine of either an airborne or earthbound backup power system. No matter the particular end-use system, a solid propellant gas generator typically includes a vessel that defines a combustion chamber within which one or more solid propellant masses are disposed. The solid propellant masses, when ignited, generate high-energy propellant gas. Depending upon the particular end-use system in which the solid gas generator is installed, the propellant gas may be supplied, or at least selectively supplied, to a rocket motor and/or reaction jets that may vary the thrust, pitch, yaw, roll or spin rate and other dynamic characteristics of a vehicle in flight, and/or to a gas turbine to generate backup power.
As is generally known, once a solid propellant mass is ignited, propellant gas generation continues until the entire mass is consumed. As is also generally known, the burn rate of a solid propellant mass may vary with the pressure in the combustion chamber. For example, if the combustion chamber pressure increases, the solid propellant burn rate increases. Conversely, if the combustion chamber pressure decreases, the propellant burn rate decreases. One way of controlling combustion chamber pressure, and thus propellant burn rate, is by controlling the effective flow area of a supply passage downstream of the combustion chamber. For example, if the effective flow area of the flow passage decreases, combustion chamber pressure increases, and vice-versa.
Various systems and methods have been developed for varying the effective flow area of a solid propellant gas generator supply passage. Such systems and methods include selectively venting propellant gas from the combustion chamber, throttling propellant gas flow using a fixed or variable area orifice, and throttling propellant gas flow via a variable position valve. Although these systems and methods are effective, each suffers certain drawbacks. For example, the present systems and methods can significantly affect overall gas generator efficiency, and may rely on fairly complex, relatively heavy, and or relatively costly components and control systems.
Hence, there is a need for a system and method of controlling solid propellant burn rate, combustion chamber pressure, and propellant gas flow that does not significantly affect overall efficiency and/or does not rely on fairly complex, relatively heavy, and/or relatively costly components and control systems. The present invention addresses one or more of these needs.